Many telephone communications systems, such as private branch exchanges, offer a feature known as “call pickup” where a first telephone may be used to answer a call that is ringing a second telephone. This generally requires that the telephones be associated with a common “pickup group” designated within the telephone system. This feature is useful in places, such as in a business office, where a receptionist might answer lines for other people when it is noticed that the lines are ringing without being answered, or where an inbound call may be answered by any one of a number of people who are in the vicinity of the ringing telephone but who have their own telephones by which to answer the call. In some arrangements, one person may be said to “cover” another person's telephone.
In some systems providing multiple line telephones, it is possible for a telephone to detect the ringing of a specific line that may normally correspond to a given person. If this call goes unanswered by the person, other people using other telephones may observe the ringing line and elect to pickup the call by selecting the ringing line and going “off-hook” to answer the call.
It is also possible to implement call pickup features in a system where relatively simple telephones are used and the telephones lack the special buttons and displays to provide visibility and access to multiple lines. By virtue of provisioning at a private branch exchange (PBX) or a switch, telephones may be assigned to common pickup groups. Thus, when one telephone belonging to the pickup group rings, another telephone belonging to the pickup group may be used to answer the call by an answering party by going off-hook and dialing a specific special sequence, such as “*55” which the switch or PBX recognizes as signifying a desire to pickup a call from another telephone in the group. Upon recognizing the call pickup sequence, the switch examines the group to identify the call causing the other telephone to ring, and connects the call instead to the answering party.
While call pickup, in general, is now well known in traditional telephony, the proliferation of data transport networks, most notably the Internet, is causing a revolution in telephony and other forms of real-time communications. Businesses that have been accustomed to having telephony traffic and data traffic separately supported over different systems and networks are now moving towards so-called “converged networks,” where telephone voice traffic and other forms of real-time media are converted into digital form and carried by a packet data network along with other forms of data. Now that the technologies are feasible to support it, voice over data transport offers many advantages in terms of reduced capital and operating costs, resource efficiency, and flexibility.
Thus, the field of telephony is turning away from the traditional use of circuit switches operating under stored program control or under the control of industry standardized intelligent network (IN) call processing. Instead, new service processing architectures (such as the so-called “softswitch” approach) and protocols (like SIP) have arisen, significantly patterned upon techniques developed for the Internet and other data networks.
Aside from cost considerations, a significant advantage and motivation for this change in service processing is the promise of enhanced new services and faster deployment of services. New packet-switched telephony networks, coupled with the aforementioned new service processing paradigms, are being designed to offer users unprecedented levels of flexibility and customization options.
Even at the periphery of the network, new generation of end user terminal devices are now replacing the traditional telephones and even the more recent PBX phone sets. These new end user terminal devices, such as those offered by Cisco Systems, Inc. and Pingtel Corporation, may connect directly to a common data network, via, for example, an Ethernet connection, and feature large visual displays to enhance the richness of the user interface.
Another significant sign of radical departure from traditional telephony relates to the manner in which destinations are expressed. Rather than using the familiar telephone number to place a call to a particular telephone station, the new paradigm relies upon identifying a party whom one is trying to reach, independent of any particular location or station address, such as a telephone number. The current trend is that this identification is alphanumeric and resembles an e-mail address or URI (universal resource identifier) as is now commonly used in other types of communication. The new telephones described above can “dial” such alphanumeric addresses.
This technique of specifying a party rather than a station ties into another novel aspect of packet-switched telephony, namely that user location is allowed to be very dynamic. By default, a given user may be associated with a particular communications terminal (telephone, cellular telephone, pager, etc.) in the traditional sense. In addition, the user may approach one of the newer types of IP telephone appliances and register his presence to receive calls at the given telephone appliance. Any inbound calls will then go to the most recently registered address. Given this mobility, the identification scheme for destination parties must be decoupled from the addressing of specific terminals. Soon, the familiar practice of memorizing a “telephone number” may become obsolete, or at least supplemented, by alternative symbolic expressions for specifying a given destination party, also known as a “terminating” party in the parlance of traditional telephony.
In the context of telephony communications systems that use SIP-compliant service processing or similar techniques to coordinate call set-up, a need arises to provide for call pickup capabilities.